Evaluation of a Food Portion Size Estimation Interface for a Varying Literacy Population.

Portion size estimation is important for managing dietary intake in many chronic conditions. We conducted a 6-week field study with nine varying literacy dialysis patients to explore the usability and feasibility of a dietary intake mobile application that emphasizes portion size estimation. Seven participants demonstrated sustained use of the application and improved their self-efficacy, knowledge, and ability to estimate portion sizes in pre- and post-study assessments. Participants reported moments when portion size information in the application differed from their prior understanding, challenging them to reconcile dissonant information. Although participants acquired new knowledge about portion sizes, they struggled to accurately estimate portion sizes in situ for most foods. Despite using the application consistently, rating it highly, and exhibiting learning, we found that self-efficacy and knowledge are not sufficient to support improved behaviors in everyday life.